Method of conditioning metal for hot forming



May 9, 1967 D. B. COFER ETAL 3,317,994

METHOD OF CONDITIONING METAL FOR HOT FORMING Filed Aug. 19, 1964 2Sheets-Sheet l INVENTORS DANIEL B. COFER GEORGE C4 WARD BY DALE D.PROCTOR METHOD OF CONDITIONING METAL FOR HOT FORMING y 1967 D. B. COFERETAL 2 sheetssheet 2 Filed Aug.

INVENTORS DANIE L B. COFER GEORGE CI WAR D BY DALE D. PROCTOR Mil 7 I? IUnited States l atent Cfilice 3,317,994 Patented May 9, 1967 3,317,994METHOD OF CONDITIONING METAL F OR HOT FORMING Daniel B. Cofer, George C.Ward, and Dale D. Proctor, all of Carrollton, Ga, assignors to SouthwireCompany, Carrollton, (221., a corporation of Georgia Filed Aug. 19,1964, Ser. No. 390,666 11 Claims. (Cl. 29-528) ABSTRACT OF THEDISCLOSURE What is disclosed herein is a method of hot-forming anon-homogenized metal which involves the compression of the metal to theextent necessary to substantially destroy the dendritic structure of themetal as an initial step in or prior to generally conventionalhot-forming. The method is disclosed in terms of compressing a copperbar to reduce its cross-sectional area by at least 36% and in terms ofusing a roll-stand positioned between a continuous casting machine anda' rolling mill to provide the necessary compression. The method resultsin a resistance to cracking and splitting during hot-forming such asthat achieved in the prior art by homogenizing the metal prior tohot-forming.

This invention relates generally to the rolling of metal and moreparticularly to a method of conditioning metal for hot-forming such asby hot rolling.

In the hot rolling of metal, cracking and splitting of the metal isfrequently encountered as the result of a characteristic commonly knownas hot shortness. Moreover, cast metal usually has internal stresses dueto nonuniform cooling rates during casting or due to straightening themetal after casting. These stresses also cause cracking and splitting ofthe metal during rolling or forming.

The cracking and splitting of metal as the result of hot shortness orinternal stresses can be avoided by homogenizing the metal prior to hotrolling. This is because homogenizing a metal disperses alloying andother elements and compounds from grain boundaries between dendriteswithin the metal into the dendrites. The result is an increase intensile strength to a degree suflicient to resist cracking and splittingbecause of hot shortness or internal stresses.

The homogenizing of a metal requires that the metal be held at atemperature above the recrystallization temperature of the metal for anextended period of time. Where the metal to be hot rolled is initiallyat room temperature, the elevated temperature and the period of time atthis elevated temperature required for homogenizing the metal areobtained simply by reheating the metal to hot rolling temperature sincethis provides time and temperature conditions sufficient forhomogenization. Where the metal to be hot rolled has not been allowed tocool to room temperature from its casting temperature, the elevatedtemperature and the period of time at this elevated temperature requiredfor homogenization of the metal can be obtained only by holding themetal at approximately casting temperature for an extended period oftime. This is commonly known as soaking. Thus, whether a metal to be hotrolled is at room temperature or at casting temperature, homogenizationof the metal prior to rolling is time consuming and frequently requiresextensive equipment and space.

Moreover, neither of the above techniques for homogenizing a metal issuited tothe continuous casting and hot rolling of metal since it isimpractical to cool and reheat continuously cast metal before it is fedto a rolling mill or to hold continuously cast metal at an elevatedtemperature for the length of time required to accomplish homogenizationas the metal is continuously fed from a casting machine to a rollingmill. Thus, the homogenization of a metal prior to hot rolling is agenerally unsatisfactory method of preventing splitting and cracking ofthe metal during hot rolling and is a particularly unsatisfactory methodof accomplishing this objective where it is desired to continuously rollcontinuously cast metal.

The invention disclosed herein substantially eliminates these and otherproblems associated with the rolling of metal in that it conditions ametal so that the metal may be rolled without any significant tendencyto crack or split even though the metal has not been homogenized andeven though the metal would crack and split in the absence ofconditioning in accordance with the invention.

'The metal to be rolled is conditioned for hot rolling by reducing thecross-sectional area of the metal without splitting and cracking to thatextent necessary to destroy the columnar dendritic structure therein.

The conditioning is accomplished at substantially hot rollingtemperature prior to hot rolling or as the initial step in hot rolling.After the metal has been conditioned in accordance with the invention,the metal may be hot rolled into substantially any shape withoutcracking and splitting of the metal occurring. This is because thedestruction of the columnar dendritic structure provides a metal havinga greatly increased tensile strength. The tensile strength attained issufiicient to prevent cracking and splitting because of hot shortness orinternal stresses and the metal is as suitable for hot rolling withoutcracking and splitting as metal which has been homogenized. Theinvention is practicularly well adapted to the continuous casting ofmetal since the required reduction of the cross-sectional area of themetal as cast without cracking or splitting is easily accomplished at arapid rate and this rate permits the metal to be conditioned for rollingas the metal is continuously fed from a continuous casting machine to arolling mill or similar apparatus.

These and other features and advantages of the invention will be moreclearly understood from the following detailed description and theaccompanying drawings in which the like characters of referencedesignate corresponding parts in all figures and in which:

FIG. 1 is a top plan view of the apparatus suitable to practice thepresent invention and positioned to condition metal being fed from acontinuous casting machine into a conventional rolling mill;

FIG. 2 is an enlarged elevational view of the compression rolls of theapparatus shown in FIG. 1;

FIG. 3 is a diagrammatic drawing of the compression rolls shown in FIG.2 illustrating with velocity triangles the velocity relationships in therolling grooves of the rolls;

FIG. 4 is a cross-sectional representation of a cast metal bar prior toconditioning for rolling in accordance with the present invention;

FIG. 5 is an enlarged view of a portion of the representation of a castmetal bar shown in FIG. 4.

FIG. 6 is a cross-sectional representation of the cast bar shown in FIG.4 after conditioning for rolling in accordance with the presentinvention.

The following detailed description discloses a specific embodiment ofthe invention but the invention is not limited to the details disclosedsince it may be embodied in other equivalent forms.

Referring to FIG. 1 and FIG. 2, the apparatus chosen for the purpose ofillustration of the present invention is seen to comprise generally abase 10, a left upright 11, a right upright 12, an upper roll 14 mountedon a shaft 15, and a lower roll 16 mounted on a shaft 18. The

rolls 14 and 16 are rotatably positioned parallel to each other betweenthe left upright 11 and the right upright 12 by shafts 15 and 18, andthe shaft 18 extends through the left upright 11 to a clutch 13 whichserves to join the shaft 18 in known manner to the drive shaft 19 of amotor 20 mounted on a platform 17 adjacent the left upright 11.

The motor 213 drives the roll 16 through the shaft 18 and the shaft 15is joined within the right upright 12 to the shaft 18 so that as theshaft 18 rotates in a particular rotational direction, the shaft 15rotates in the opposite rotational direction and at the same rotationalspeed as the shaft 18. Thus, the motor 2d serves to rotate the rl1s14and 16 in opposite directions at substantially identical rotationalspeeds.

4 The spacing between the rolls 14 and 16 is adjustable by rotation of awheel 23 at the upper end of a shaft 27 extending from within the rightupright 12. It will now be understood that those features of theapparatus described above are generally conventional with two-rollrolling stands as known to those skilled in the art and that it is forthis reason that known details of construction have not been described.It will also be understood that When a cast metal bar 21 is receivedfrom a casting means such as a casting machine 49 of known type having awheel 41 and a belt 42 and inserted between the rolls 14 and 16 from theleft as viewed in FIG. 1, the rolls 14 and 16 reduce the cross-sectionalarea of the metal bar 21 and force the metal bar 21 to the right to bereceived by a hot-forming means such as a conventional rolling mill 22or similar compressing means positioned as shown in FIG. 1. w

Positioned above the base in the path of the metal bar 2121s it movesthrough the rolls 14 and 16 are a pair of guide rolls 38 and 39rotatably carried by supports 45 attached to the base 10. The guide roll38 is shaped to receive and support the metal bar 21 as it approachesthe rolls 14 and 16 and the guide roll 39 is shaped to receive the metalbar 21 as it exits the rolls 14 and 16 to be fed to a rolling mill 22 orsimilar apparatus.

As is best seen in FIG. 2, each of the rolls 14 and 16 has a groove 30having the shape of a semi-ellipse. Together the grooves 30 define anelliptical rolling channel 29 in which the metal bar 21 is compressed asit passes between the rolls 14- and 16. This rolling channel 29 servesto prevent excessive spreading of a metal bar 21 having thecross-sectional shape shown in FIG. 4 as it is compressed by the rolls14 and 16 to produce the crosssectional shape of the metal bar 21 shownin FIG. 6.

Moreover, as is best shown in FIG. 3, the rolling channel 29 provideslinear speed relationships in the metal bar 21 as the metal bar 21passes between the rolls 14 and 16 which physically prevent cracking andsplitting of the metal bar 21 as the result of abrupt changes invelocity Within the metal bar 21 as it is being rolled by the rolls 14and 16. This is because the elliptical shape of the rolling channel 29causes the rolls 14 and 16 to have different linear tangentialvelocities as they engage different portions of the metal bar 21. Asindicated by the arrows 32 and 34 in FIG. 3, that portion of each groove31 nearest the axis of rotation of rolls 14 and 16 has the smallesttangential velocity and those portions of each groove 30 at its outeredges have the greatest tangential velocity.

It will be understood that those portions of each groove 36 between thatportion indicated by an arrow 32 as hav ing the smallest tangentialvelocity and those portions indicated by an arrow 34 as having thegreatest tangential velocity will progressively increase in tangentialvelocity from the smallest tangential velocity to the largest tangentialvelocity. It will also be understood that this velocity relationshipwithin the rolling channel 29 tends to force the outer edges of a metalbar 21 inwardly toward the center of the rolling channel 29 when themetal bar 21 is fed between the rolls 14 and 16. From the foregoing, itwill be seen that the apparatus provides a means for reducing thecross-sectional area of a metal bar 21 while at the same time physicallypreventing cracking or splitting of the metal bar 21 even though themetal in the metal bar 21 has not been homogenized.

The cross-section of the metal bar 21 after passing between the rolls 14and 16 is substantially that shown in FIG. 6. The metal bar 21 havingthis cross-sectional shape is particularly well adapted for rolling in arolling mill 22 or similar apparatus into rod or other forms. However,the purpose of the rolls 14 and 16 is to substantially reduce thecross-sectional area of the metal bar 21 without cracking or splittingoccurring, and it will be understood that rolling channels 29 havingother configurations which physically prevent the splitting or crackingof the metal bar 21 as its cross-sectional area is reduced Willcondition the metal bar 21 for subsequent hot rolling into substantiallyany cross-sectional shape without cracking or splitting. This is becausethe size of the rolling channel 29 is selected so that the reduction inthe cross-sectional area of the metal bar 21 as it passes between therolls 14 and 16 is sufficientiy great to destroy the dendritic structureof the metal bar 21, and because it is this particular amount ofreduction in the crosssectional area of the metal bar 21 withoutsplitting or cracking of the metal bar 21 which conditions the metal bar21 for conventional rolling operations. Thus, any apparatus arrangementsuited to reducing the cross-sectional area of a metal bar 21 to adegree suflicient to destroy the dendritic structure within the metalbar 21 while physically preventing the cracking or splitting of themetal bar 21 is suitable for conditioning the metal bar 21 for hotrolling.

From the foregoing description of an embodiment of the invention, itwill be seen that the invention conditions a metal bar 21 by compressingor squeezing the metal bar 21 so as to reduce the cross-sectional areaof the metal bar 21 while at the same time physically preventingcracking or splitting of the cast bar 21 as it is compressed. Thecompressing or squeezing is accomplished prior to hot rolling with themetal bar 21 in substantially its as cast condition a hot-formingtemperature or as the initial step in hot rolling the metal bar 21. Asshown in FIG. 6, the cross-sectional shape of the metal bar 21 afterpassing through that embodiment of the apparatus described hereinresembzes an ellipse, and it has been found that such a cross-sectionalshape provides a metal bar 21 'which permits the metal bar 21 to beeasily rolled by a rolling mill 22, or similar apparatus, into the shapeof a rod or any other desired shape. However, it will be understood thatthe cross-sectional shape of the metal bar 21 before and after passingbetween the rolls 14 and 16 may be any of a wide variety of shapes. Thisis because of the rolling channel 29 shape may be any shape whichreduces the cross-sectional area of the metal bar 21 While physicallyrestricting and controlling the side spread of the metal bar 21 so as toprevent splitting and cracking of the metal bar 21.

Regardless of the rolling channel 29 shape selected to physicallyprevent cracking and splitting of the metal bar 21, the inventionreduces the cross-sectional area of the metal bar 2.1 to that extentnecessary to destroy the dendritic structure of the metal bar 21. Theamount by which the cross-sectional area of the metal bar 21 must bereduced to destroy the dendri-tic structure of the metal in the metalbar 21 depends upon the particular metal from which the metal bar 21 iscast and the cross-sectional area of the metal bar 21 before passingbetween the rolls 14 and 16. Accordingly, it will be understood that thespacing between the rolls 14 and 16 is varied in accordance with themetal in the metal bar 21 and the cross-sectional area of the metal bar21 before conditioning in accordance with the invention.

For a continuously cast metal bar 21 of cop-per which has internalstresses, which exhibits the characteristic of hot shortness to anundesirable degree, or which has both internal stresses and thecharacteristic of hot shortness to an undesirable degree, it has beenfound that a reduction in the cross-sectional area of the metal bar 21by at least approximately 36 percent with a single compression willresult in the destruction of the dendritic structure of the copper. Thereduction is accomplished at substantially the hot rolling temperatureof copper and a metal bar 21 of copper may be subsequently hot rolledwith a plurality of sequential compressions into substantially anydesired form without undesirable cracking or splitting.

The amount of reduction of the cross-sectional area of the metal bar 21where the metal bar 21 is of a metal other than copper will be readilyapparent to those skilled in the art or may be readily obtainedempirically using known metallurgical techniques. The temperature atwhich the reduction is accomplished will be substantially the hotrolling temperature of the metal and will also be readily apparent tothose skilled in the art.

Regardless of the metal from which the metal bar 21 is cast, once thedendritic structure of the metal bar 21 is destroyed, the metal bar 21is conditioned for hot rolling in a rolling mill 22 or other apparatususing conventional hot rolling techniques. The conditioning of the metalbar 21 by the invention is represented by a comparison of FIG. 4 andFIG. 5 with FIG. 6. In FIG. 5, the cast bar 21 is represented as havingcolumnar dendrites 2-4 and with segregated alloying and other elementsand compounds trapped at the grain boundaries 25 of the dendrites 24.

FIG. 6 represents the metal bar 2-1 represented in FIG. 4 and FIG. 5after the metal bar 21 has been conditioned in accordance with theinvention. .It will be seen from FIG. 6 that in the metal bar 21', thedendritic structure has been completely destroyed. This eliminates thegrain boundaries at which the alloying and other elements and compoundsindicated by the letter S in FIG. 5 were segregated and substantiallyincreases the tensile strength of the metal in substantially the samemanner as homogenizing the metal. As a result, the tensile strength ofthe metal in the metal bar 21 is sufficiently great to resist crackingand splitting because of hot shortness, internal stresses, or both whenthe metal bar 21 is subsequently hot rolled.

From the foregoing description of the invention disclosed herein, itwill now be understood that when a metal bar 21 having internal stressesor substantial amounts of elements and compounds causing hot shortnessis conditioned for hot rolling by the destruction of.

the dendritic structure prior to rolling, the metal bar 21 maybe hotrolled in any suitable conventional apparatus such as the rolling mill22 without cracking or splitting of the metal bar even though the metalis not homogenized prior to rolling in the rolling mill 22. Thus, theinvention is ideally suited to the rolling of continuously cast metalssince apparatus may be used in combination with the rolling mill 22 asshown in FIG. 1 to condition and feed the metal bar 21 continuously intothe rolling mill 22 from a casting machine 40'. When the inventiondisclosed herein is used with a rolling mill 22 it provides a convenientand elfective rolling operation in which the metal bar 21 is efiicientlyconditioned and rolled.

It will of course be understood that the present invention is in no waylimited to the particular device here presented by way of illustration,but many changes and modifications may be made, and the full use ofequivalents resorted to Without departing from the spirit or scope ofthe invention as defined in the appended claims.

What is claimed as invention is:

1. In a method of hot-forming non-homogenized continuously cast copper,the steps of passing said copper in substantially its as cast conditionand at a hot-forming temperature from a casting means to a hot-formingmeans, conditioning said copper for subsequent hot-forming bysubstantially completely destroying the dendritic struc ture of saidcopper as said copper passes between said casting means and saidhot-forming means by a single compression of said copper to reduce itscross-sectional area by at least 36%, and hot-forming said copper insaid hot-forming means with a plurality of sequential compressions.

2. In a method of hot-forming a non-homogenized continuously cast copperbar, the steps of feeding said bar at a hot-forming temperature to acompressing means, initially compressing said bar by a singlecompression of said bar to the extent necessary to reduce itscross-section by at least 36% and to substantially destroy its dendriticstructure, and subsequently compressing said bar by a plurality ofsequential compressions in each of which the cross-section of said baris changed to the extent necessary to provide a hot-formed producthaving a predetermined cross-section.

3. The method of claim 1 including restricting said copper during saidconditioning said copper so as to prevent cracking of said copper.

4. The method of claim 1 in which said conditioning said copper includespassing said copper between rolls,

in a roll-stand.

5. The method of claim 1 in which said hot-forming means is a rollingmill having a plurality of roll-stands and in which said hot-formingincludes passing said copper through said roll-stands in sequence.

6. The method of claim 4 in which said rolls define an ellipticalrolling channel shaped to restrict the lateral spread of said copper.

7. The method of claim 1 in which said casting means is a casting Wheelof a casting machine and in which said hot-forming means is a rollingmill having a plurality of roll-stands.

8. The method of claim 2 including restricting said bar during saidinitially compressing said bar so as to prevent cracking of said bar.

9. The method of claim 2 in which said single compression is by passingsaid bar between rolls in a rollstand.

10. The method of claim 9 in which said subsequently compressing saidbar is by passing said bar between rolls in a plurality of roll-stands.

11. The method of claim 9 in which said rolls define an ellipticalrolling channel shaped to restrict the lateral spread of said bar.

References Cited by the Examiner UNITED STATES PATENTS 2,264,288 12/1941Betterton -76 X 2,710,433 6/1955 Properzi 22-200.1 X 3,146,525 9/1964Bongiovanni 29-528 3,234,052 2/ 1966 Wikle 148-2 X 3,259,975 7/1966Chapman 29-528 3,274,681 9/1966 Lohman 29-528 OTHER REFERENCES Part 2:Continuous Casting-Progress Report on the Properzi Process by J. B.Russell, Modern Metals, April 1964, pp. 56 and 58.

JOHN F. CAMPBELL, Primary Examiner. R. F. DROPKIN, Assistant Examiner.

2. IN A METHOD OF HOT-FORMING A NON-HOMOGENIZED CONTINUOUSLY CAST COPPERBAR, THE STEPS OF FEEDING SAID BAR AT A HOT-FORMING TEMPERATURE TOACOMPRESSING MEANS INITIALLY COMPRESSING SAID BAR BY A SINGLECOMPRESSION OF SAID BAR TO THE ENTENT NECESSARY TO REDUCE ITSCROSS-SECTION BY AT LEAST 36% AND TO SUBSTANTIALLY DESTROY ITS DENDRITICSTRUCTURE, AND SUBSEQUENTLY COMPRESSING SAID BAR BY A PLURALITY OFSEQUENTIAL COMPRESSION IN EACH OF WHICH THE CROSS-SECTION OF SAID BAR ISCHANGED TO THE EXTENT NECESSARY TO PROVIDE A HOT-FORMED PRODUCT HAVING APREDETERMINED CROSS-SECTION.